Ca-carboxymethyl xanthan gum mini-matrices: Swelling, erosion and their impact on drug release mechanism

• Ca2+ ions cross-linked carboxymethyl xanthan gum mini-matrices.
• Increase in cross-linking altered the viscosity of gel layer around matrices.
• Increase in cross-linking decreased swelling and increased erosion.
• Drug release shifted from anomalous to Super Case II transport.

The effect of Ca2+ ion concentration on swelling, erosion, and drug release mechanism of Ca2+ ion cross-linked carboxymethyl xanthan gum (Ca-CMXG) matrices was investigated. By adding CaCl2 solution, carboxymethyl xanthan gum (CMXG) was converted into Ca-CMXG matrix, which was evaluated for swelling, erosion and drug release in different dissolution media. The amount of Ca2+ ion alters the viscosity of gel layer formed around the matrices resulting in decreased water penetration into swollen layer. The changes in amount of Ca2+ ion considerably influenced the swelling and erosion of the matrix leading to different drug release profiles. The simultaneous swelling and erosion of matrices that were controlled by the degree of cross-linking prejudiced the drug release mechanism. The release data fitted well into the Korsmeyer–Peppas equation and the combined effect of diffusion and erosion described the overall drug transport mechanism.